| | Precipitation | Soil moisture| Data sources | Explanation of terms
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Summary
Since the last, August 10, 2008, drought report, precipitation accumulations and daily temperature regimes have generally been at least near normal across most of the reporting area, with the exception of the northern portions of the Peace Region and west central parts of the Northern Region where moderately low precipitation accumulations were recorded. Much of the reporting area received at least 30 mm of precipitation, with some large and widely scattered areas receiving above 70 mm. Areas receiving less than 20 mm include parts of the northern Peace Region, the west-central and north-eastern parts of the Northern Region, and many locals in the western half of the Southern Region.
Average daily mean temperatures, relative to long term normal, during the past 15 days, were at least near normal across most of the reporting area with some exceptions, where moderately low average temperatures prevailed (Figure 6).
Growing season precipitation accumulations relative to the long term normal to date, (April 1 to Sep 1, 2008) are at least near normal across the Southern Region, most of the Central Region, and the south-eastern and the north-central parts of the Northern Region as well as in a few isolated pockets in the central and northern parts of the Peace Region. Precipitation accumulations in the rest of the reporting area were generally moderately low with parts of the western Peace Region and central portions of the Northern Region grading to extremely low.
Currently, soil moisture reserves across much of the west half of the plains areas, the north-eastern parts of the Northern Region and the western and northern parts of the Peace Region are estimated to be below 25 mm, while reserves across the rest of the reporting area are generally in the 25 to 50 mm range, with the exception of the western parts of the Central Region where reserves were more than 75 mm.
Soil moisture reserves relative to long-term normal were at least near normal across the Southern and Central Regions, and across some areas in eastern parts of Northern Region. Across the Northern Region low reserves are found in the northeast as well as in the western half of the region. In the central parts of the Northern Region large deficits that range from low to extremely low are extensive with the direst areas found in the north and south east of the city of Edmonton. Across the Peace Region reserves are near normal in the centre and grade to extremely low in parts of the north, and then to moderately low in the west and south east.
A large selection of related maps can be found at http://www.agric.gov.ab.ca/acis, under the Quick Viewer tab. Note these maps are updated once a week (usually by Wednesday) providing updates between drought reports.
Precipitation
Precipitation since the August 10, 2008 Drought Report (Figure 1)
Since the last report (August 10, 2008), precipitation accumulation of more than 30 mm were received across most parts of the reporting area, with two distinct wide bands in the Northern and Central Regions recording more than 70 mm. Areas receiving less than 20 mm included the central and eastern parts of the Northern Region, northern parts of the Peace Region, and several pockets in the southern parts of the Central Region and western half of the Southern Region.
Peace Region: Precipitation accumulations across the region graded from 40 to 60 mm across the south and 10 to 30 mm across the north. The highest precipitation accumulation was recorded at Grande Prairie A station (59.0 mm) in the south, followed by Peace River A station (58.2 mm) in center, and the lowest at Fort Vermillion RS station (8.4 mm), followed by High Level A station (10.0 mm), both located in the northern parts of the region.
Northern Region: Precipitation accumulations across the region varied widely with accumulations across the west half and the north-eastern portions of the region ranging from 10 to 50 mm. Significant accumulations (greater than 70 mm) were recorded in a wide band extending from the Lac La Biche County in the northeast to the M.D of Provost in the south. The highest accumulations of precipitation in the region were recorded at Lac La Biche A station (104.0 mm), followed by the Hughenden AGCM station (97.8 mm) in the southeast corner, whereas the lowest accumulations were recorded at the Cold Lake A station (12.4 mm) in the northeast, followed by Fort Assiniboine AGCM station (14.1 mm) in the west.
Central Region: The greatest amounts of precipitation (60 to 100 mm) were found in a wide band extending from Mountain View County in the southwest up to the County of Stettler in the north. In the east-central parts of the region, accumulations were the lowest, with less than 20 mm being recorded in Special Area 2. Elsewhere, precipitation ranged between 40 to 70 mm, with the exception of the extreme southeast where more than 90 mm was recorded. The highest precipitation accumulation was recorded at Stettler AGDM station (99.8 mm) in the north, followed by Atlee AGCM station (98.0 mm) in the southeast, and the lowest accumulations were recorded in the southeast, at the Cop Upper station (5.5 mm) followed by Pollockville AGDM station (16.5 mm).
Southern Region: Precipitation accumulations graded from a high of 50 to 80 mm in the east to a low of 10 to 20 mm in the southwest, as well as in some isolated pockets in the North. The highest accumulations were recorded at Medicine Lodge station (76.1 mm), followed by Pakowki Lake AGDM station (68.4 mm), both located in the southeast corner, whereas, the lowest accumulations were at the Pincher Creek station (9.5 mm) followed by Livingstone A station (10 .2 mm) in the northwest.
Growing Season Precipitation Accumulation relative to Long Term Normal (1961 - 2005) (Figure 2)
Growing season precipitation accumulations relative to long term normal to date, (April 1 to Sep 1, 2008) are at least near normal across the Southern Region, most of the Central Region, and the south-eastern and the north-central parts of the Northern Region, as well as in two isolated pockets in the northern parts of the Peace Region. Accumulations across the rest of the reporting area were moderately low or worse, with several areas grading to very low and extremely low. Those areas classified as extremely low can be found in the north-western Peace Region and southeast of the City of Edmonton in the Northern Region.
Peace Region: Growing season precipitation accumulations relative to long term normal varied from at least near normal accumulations in pockets located in the centre and north, to very low and extremely low conditions in the western parts of the region, affecting the Saddle Hills County and the M.D's of Fairview, Spirit River, and Clear Hills.
Northern Region: In general, growing season precipitation accumulations relative to normal across most of the region were moderately low or worse, grading to lows of very low and/or extremely low in isolated pockets, the largest of which is located in the neighbouring counties south and southeast of the city of Edmonton. In contrast, the north-central and south-eastern portions of the region have had near normal growing season precipitation accumulations to date.
Central Region: Growing season precipitation accumulations relative to long term normal were at least near normal across most of the region, with the exception of the northwest and a pocket in the east central portions of the region, where moderately low accumulations were recorded.
Southern Region: In general, growing season precipitation accumulations relative to the long term normal are at least near normal across most of the region, with large areas grading to moderately high, and parts of the northwest and northeast grading to high.
Average Precipitation Accumulations for September (Figure 3)
September marks the transition between the wet season (May - August) and the drier winter months (October - March). During this month precipitation typically declines significantly, with precipitation totals ranging from just over 20 mm in the Special Areas to less than 60 mm in the Swan Hills and Foothills. Provincially, on average about 9 percent of the annual precipitation falls in September. September and October are important months for soil moisture recharge in Alberta, since moisture losses due to evaporation and plant water demands are reduced significantly. Fall and spring rains help to replenish soil moisture for the following growing season, thus those areas that are currently abnormally dry will need above average precipitation (post harvest) over the next several months to help build soil moisture reserves for next spring.
Soil Moisture in the Agricultural Regions of Alberta (Figure 4 and Figure 5)
Currently, soil moisture reserves across most of the west half of the plains reporting area and the north-eastern parts of the Northern Region and the western and northern parts of the Peace Region are estimated to be below 25 mm. Soil moisture reserves across the rest of the reporting area are generally in the 25 to 50 mm range, with the exception of the western parts of the Central Region where reserves are greater than 75 mm. Relative to normal, reserves south of Red Deer are at least near normal, with large areas grading to high or above. In the Northern and Peace Region reserves are generally moderately low or worse with central parts of the Northern Region and northern parts of the Peace Region grading to very low and extremely low.
Peace Region: Soil moisture reserves in the region graded from 25 to 50 mm across the south half of the region to below 25 mm in the north half. Modeled soil moisture reserves relative to long term normal grade from near normal reserves, in the central and eastern parts of the region to low and extremely low reserves in the north and to moderately low reserves in the rest of the region.
Northern Region: Much of the Region's soil moisture reserves are estimated to fall below 25 mm, with the exception of band in the 25 to 50 mm range that extends from Lac La Biche County in the north down to the M.D. of Provost in the south. Relative to long term normal, reserves in the west half and in the north-eastern parts of the region are at least moderately low to low with large parts in the central parts of the region grading to very low, and is some areas down to extremely low.
Central Region: Soil moisture levels in the region graded rapidly down from a high of above 75 mm in the west to a lows of less than 25 mm across most of the central parts of the region and then up again to 25 to 50 mm in the east. Relative to the long-term normal, reserves are at least near normal across the entire region with parts of the southwest and extreme east grading to very high.
Southern Region: Soil moisture levels in the region graded sharply down from more than 75 mm in the west to less than 25 mm across most of the central parts of the region and then again up to 25 to 50 mm range in the east. Modeled soil moisture reserves relative to long-term normal grade from near normal in the west half of the region to very high in the east and southeastern parts of the region with some areas in the extremely high range.
Data Sources:
Near Real Time Weather data
Daily and hourly near-real-time raw weather data is brought in via daily data feeds from Alberta Environment (AENV) and Environment Canada (EC). The data undergoes a preliminary computer assisted QA/QC check performed by Alberta Agriculture and Rural Development (ARD) staff. Suspicious values are checked and verified and daily missing values are filled using archived data from AENV databases or from the EC web site. If daily data is still missing, it is estimated using data from nearby stations. Maps describing current conditions are based on preliminary data that is subject to change under further review by ARD, AENV and EC.
Historical Weather data
Historical weather data was provided by Environment Canada. This data was then converted to a 10 km daily gridded weather data set that used all available daily data to generate historical climate and soil moisture normals.
Explanation of Terms
Precipitation Accumulation - Frequency of Occurrence
Precipitation accumulation, expressed as a frequency of occurrence are computed for various periods and can be found on our web site at www.agric.gov.ab.ca\acis, under the Quick Viewer tab. Maps are routinely produced for the following periods:
- Past 365-days
- Past 180-days,
- Past 90-days
- Past 30-days,
- Growing season to date -Starting April 1
- Cold Season to date- Starting October 1
Selected maps from this series are included in this report.
Precipitation accumulations for each period are then determined by ranking the precipitation accumulation during similar period dating back from 1961 to present. The current accumulation is compared to the ranked values, yielding the frequency of occurrence, based on percentiles. The percentile points were then put into arbitrary but intuitive classification fields that describe the current state as drier, near or wetter than the long term normal. The resulting map thus answers the question "how often does this occur?" The classifications are as follows:
| Description | Frequency of Occurrence |
| extremely low | drier than this, on average, less than once in 25-years |
| very low | drier than this, on average, less than once in 12-years |
| low | drier than this, on average, less than once in 6-years |
| moderately low | drier than this, on average, less than once in 3-years |
| near normal | on average, this occurs at least once in 3-years |
| moderately high | wetter than this, on average, less than once in 3-years |
| high | wetter than this, on average, less than once in 6-years |
| very high | wetter than this, on average, less than once in 12-years |
| extremely high | wetter than this, on average, less than once in 25-years |
This same scheme is then used for similar maps of soil moisture and snow pack accumulation so that comparisons can readily be made across the various map types.
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SWE) are modeled for stubble fields. SWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SWE is computed from precipitation and subsequent losses due to blowing, sublimation and snow melt processes.
In the model, if precipitation falls when the mean daily temperature is below 2 °C that precipitation is estimated to be in the form of snow. If precipitation if estimated to fall as snow then to simulate drifting, only 70 percent of the total precipitation is allowed to accumulate resulting in a 30 percent loss due to snow "blow off". If precipitation occurs as rain on an existing snow pack, it is added directly to the snow pack as SWE.
Soil moisture (reported during the growing season months only)
Soil moisture is measured as millimetres (mm) of plant available water. Plant available water is approximately half of the total water that can be measured in the soil. Soil moisture is reported on from May through to October.
The crop gets the moisture it requires from the reserve of soil moisture, which in turn is replenished by precipitation. Soil moisture is a valuable indicator of drought potential because it indicates the reserve of water available to the crop at a given point in time. During peak growing periods, soil moisture reserves are consumed quickly and must be replenished frequently by rainfall. Poor soil moisture reserves during peak water use indicate a high risk of immediate crop stress. Prolonged stress becomes drought and results in significant unrecoverable yield loss.
Because the climate varies across Alberta, comparing current moisture levels to normal levels provides a valuable indicator of drought risk that can be applied to all localities during the frost-free season. Current soil moisture levels are compared against soil moisture levels for the same day in each year from 1961 to present. The frequency of occurrence is computed based on the percentile points, using the same method that was used for similar maps that were generated for precipitation. The frequency of occurrence is then plotted using the same class scheme as is used in the long-term (hydrologic) drought map (see table above). Soil moisture reserves with a modifier of low, indicate a need for more precipitation to restore reserves.
Soil moisture needed to return to average spring or fall conditions
Soil moisture needed to return to normal spring or fall conditions is computed by subtracting average soil moisture (spring or fall), computed using model runs dating back from 1961 from current soil moisture conditions. This yields the amount of recharge needed to bring current soil moisture levels to average. Historic model runs are then analyzed to determine how many years since 1961 that soil moisture recharge was similar to or greater than that currently needed. The number of years that this occurred is then used to compute the probability of returning to average. However, currently this process is unable to account for snow currently existing on the ground and as such is not as accurate where snow packs exist.
Report prepared by the Drought Reporting Team
Ralph Wright, Daniel Itenfisu and Isabel Simons-Everett
Alberta Agriculture, and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on September 4, 2008.
Drought analysis is currently scheduled at monthly intervals between October 31 and April 31, and twice monthly from May 1 to September 30. This report updates the previous report of August 10, 2008. |
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